惠康現金卷和百佳現金卷找誰買最平?

I want to buy wellcome & park'n shop cash coupons (no limitations, just like cash) but I want the cheapest way to buy eg can buy less amount of coupons for 8折

anyone knows who can sell - how to find his/her contact?

long term to buy, how should I find the best seller (genuine coupons, long/no expiry date, buy less coupons, more discount)?

I need contact numbers & emails, thanks

also if sogo/wing on/jusco/city super/mannings/Watsons, which sellers can offer best prices?